1. Field of the Invention
The present invention relates generally to the field of gear reduction apparatus. More particularly, the invention relates to internal, double enveloping planetary worm gear double reduction devices.
2. Description of the Relevant Art
A number of devices are known which translate a high speed, low power input into a low speed, high power output. This multiplication of the input twisting force (i.e. torque) through a sacrifice in input speed is achieved through a process known as gear reduction.
A typical planetary gear reduction consists of three concentric parts: a sun gear at the center, an internal gear, and an intermediate carrier. The carrier has a set of planetary gears which engage both the internal gear and the sun gear. In operation, input power may be applied to the internal ring, the planetary gears on the carrier or the sun gear, and the output may be taken from either of the other two members with the third member remaining stationary. By virtue of the concentric design the central axis for the input, the output, and the stationary member, is also the axis of rotation.
Each of the above gears is essentially a circular member having a spaced array of teeth. The teeth and the spaces between them are arrayed to engage the teeth and spacing situated on the gear it interacts with. Since the gears are essentially circular each interacting gear effectively rolls in the same plane and in relation to each other. Thus the gears rotate in a plane which is essentially perpendicular to the input and output shafts.
In addition to planetary gear reduction, reduction also has been accomplished utilizing worm gear sets. Worm gear sets generally consist of a worm and a worm wheel. The worm has screw-like threads cut upon its surface and the worm wheel includes gear teeth spaced about its circumference designed to engage the threads of the worm wheel. The worm is tangent to the circumference of the worm wheel. Thus the axis of rotation of the worm gear is perpendicular to the axis of rotation of the worm wheel.
In operation, the threads on the worm engage the teeth on the worm wheel. Thus, as the worm rotates, the worm wheel is driven in a circular path through a sliding action between the threads and the teeth.
The most basic worm gear assembly utilizes a single throated worm gear set. In this set, the throated portion of the worm wheel envelops the worm. The envelopment is such that effectively only one tooth of the worm wheel is engaged at one time by the worm.
A more advanced worm gear assembly utilizes a double enveloping worm gear set. This consists of an hour glass shaped worm and a throated worm wheel. The hour glass shape of the worm provides a second envelopment. Consequently, this gear set is called a double enveloping worm gear set. The double envelopment provides for multiple tooth engagement. Thus the double enveloping gear set is inherently stronger than the single throated worm gear set.
The invention disclosed in this application is an internal double enveloping, planetary worm gear set. It incorporates features which represent an advancement over the both double enveloping worm gear sets and the planetary gear sets discussed above. A principal advantage afforded is an increase in the number of teeth utilized at any one time. This allows the use of a smaller gear set than has been used before. Additionally, this invention allows the utilization of the diameter of the worm wheel, whereas previous worm gear sets could utilize only the radius.